Funneled electron multiplier



- March 30, 96 G. w. GOODRICH ETAL 3,176,178

FUNNELED ELECTRON MULTIPLIER Filed Sept. 19, 1962 3 Sheets-Sheet lINVENTORS T GEORGE M. GOODR/CH BY JAMES R. lG/VATOWSK/ JAMESE. NURMANJR.

March 5 G. GOODRICH ETAL 3,176,178

FUNNELED ELECTRON MULTIPLIER Filed Sept. 19, 1962 3 Sheets-Sheet 2 1 1/I l z z 1 1 if 41 40 T HIIIIIIIIHQ GAIN I 200 300 I 400 500 600 700 800.900 VOLTS POTENTIAL- ACROSS THE TUBE E N05 INVENTORS GEORGE M. GOODR/CHBy JAMES R lG/VATOWSK/ JAMES E. NORMAN JR.

ATTOR/V Y March 5 s. w. GOODRICH ETAL 3,176,178

FUNNELED ELECTRON MULTIPLIER Filed Sept. 19, 1962 3 Sheets-Sheet 3 FTg.6

INVHVTORS GEORGE W. GOODR/CH By JAMES R. IGNATOWSK/ JAMES E. NORMAN JR.

A T TORNE Y United States Patent Ofi ice 3,176,178 Patented Mar. 30,1965 3,176,178 FUNNELED ELECTRON MULTIPLIER George W. Goodrich, OakPark, and James R. Ignatowski,

Warren, Mich., and James E. Norman, Jr., Huntsville,

Ala., assignors to The Bendix Corporation, Southfield,

Mich., a corporation of Delaware Filed Sept. 19, 1962, Ser. No. 224,7428 Claims. (Cl. 313-104) This invention pertains to a funneled electronmultiplier having a continuous resistive or semi-conductive coatingalong the walls thereof with a voltage source connected to the ends ofthe multiplier to provide a continuous potential drop along the walls ofthe multiplier.

This invention is an improvement over the electron multiplier disclosedin copending application, US. Patent No. 3,128,408, entitled ElectronMultiplier, issued April 7, 1964, to G. W. Goodrich and W. C. Wiley. Theelectron multiplier in the aforementioned copending applicationcomprises a tube or channel having a large length to diameterratio, inthe order of ten to one for every power of ten of multiplicationdesired, which'has a coating on the inside thereof of a resistivenature. A potential is then applied to the resistive coating acrossopposite ends of the tube or channel to provide a voltage drop thereinwhich accelerates electrons introduced into the low voltage end of thetube. Since the tube has a large length to diameter ratio, the randomvelocities of the electrons entering the tube are suflicient to causethe electrons'to impact on the walls 'of the tube.

This invention improves over the previous construction by introducing afunneling or convergence to the walls of the tube so that the incomingelectrons are more likely to strike the wall of the tube near theincoming end of the tube to improve electron multiplication.

Also, since the input area is larger than the output area, larger imagesmay be reduced to smaller areas. Also, the input area may be smallerthan the output area, resulting in magnification.

By connecting a plurality of funneled channels into The embodiment inFIGURES 1 and 2 will first be considered. Funneled channel 21 has aresistance coating 22 formed interiorly thereof. Coating 22 has 10 ohmsper square in this embodiment. A potential of minus 1,000 volts isconnected to coating 22 at end 23 of channel 21. The other end ofresistance coating 22 at end 24 of channel 21 is connected to ground anda circular collector 25 at a potential of 100 volts is placed adjacentend 24 to collect the multiplied electrons.

Application of potential to the ends of resistive coating 22 causes apotential drop thereacross, thereby forming equipotential lines 26 andelectric field lines 27 which are perpendicular thereto within theenclosed volume.

The equipotential lines 26 are slightly curved due to end effects andthe increasing potential gradient towards the small end of the channel.The particles to be multiplied, which in this embodiment are electronsfrom a photocathode in an image intensifier, are directed into theenlarged end 23 of tube 21 where they are accelerated along electricfield lines 27 until they strike secondary emissive resistive surface 22at which point they are multiplied due to the secondary electrons whichare released by the energy of impact.

' With the'construction shown in FIGURES 1 and 2 it is seen that theprobability of incoming electrons striking the walls or coating 22 isincreased over a tube having parallel sides.

adjoining rows, an array is formed; and by placing a photocathode at thelarge end of the array and a phos phorous screen at the small end, animage intensifier is provided which can reduce an image focussed on thephotocathode. Conversely, reversing the direction of the array providesan image intensifier which magnifies the image focussed on thephotocathode. In this latter case, however, there is not as great apossibility that the electrons will strike a wall of the tube since thewalls are flared in the direction of the electron travel. For thisreason, a funnel-flare may be used with the funnel being shorter thanthe flare.

These and other objects and advantages of this invention will becomemore apparent when preferred embodiments are considered in connectionwith the drawings, in which:

FIGURE 1 is a perspective view of a first embodiment of this invention;

FIGURE 2 is a longitudinal cross section of FIGURE 1 shown with a sourceof particles to be multiplied and a collector;

FIGURE 3 is an array of tubes like that shown in FIGURE 1 which arefused together;

FIGURE 4 is an array of channels which are funneled at one end only andfused together with the funneled ends all at one end of the array;

FIGURE 5 is a graph showing the gain characteristics of a funneledchannel versus a parallel wall channel; and

FIGURE 6 is a longitudinal cross section of a tube having afunnel-flare.

The secondary electrons are then accelerated by field 27 into anotherportion of surface 22 to cause additional multiplication. A collector 25receives the multiplied particles and directs them to a meter orrecorder or in the case of an image intensifier, the collector 25 is aphosphorus screen and changes the energy of the multiplied particlesinto light energy.

' The conical tube 21 is formed by taking a longitudinal tube, heating,and then forcing over a conical mandrel until the desired shape isobtained. The glass used in tube 21 has a high lead content such as 25percent or more of lead oxide so that when hydrogen gas is passedthrough ata temperature of between 345 to 375 degrees centigrade forseveral hours, the resistance coating 22 is formed. In the embodiment ofFIGURES 1 and 2 the angle alpha of the flared sides is about 16 degrees;the diameter at end 24 is about .040 inch, and the diameter at end 23 isabout .4 inch while the length of the tube is about 1.3 inches.

. Ends (23 and 24) is shown on the abscissa.

The multiplying characteristics of the tube shown in FIGURES 1 and 2 isindicated in FIGURE 5 where Gain, or Input over Output, is plotted alongthe ordinate on a logarithmic scale and Potential Across the Tube CurveA shows the characteristics for the conical channel 21 having a funnelangle of about 16 degrees while Curve B shows the characteristics of acomparable parallel wall channel.

The voltage gradient of the cone 21 gradually becomes steeper as thesrrraller end 24 is approached since the resistance per longitudinalinch along tube or channel 21 increases as the cone becomes smaller.

FIGURE 3 shows array 31 of a plurality, which may number in thethousands, of channels 21 fused together. Techniques for fusing channelstogether are illustrated in copending applications U.S. Serial No.116,189, Image intensifier Array, filed June 9, 1961, by I. R.Ignatowski and R. R. Thompson; U.S. Serial No. 117,651, ImageIntensifier Array, filed June 16, 1961, by G. W. Goodrich and I. R.Ignatowski; U.S. Serial No. 116,044, Image Intensifier Array," filedJune 9, 1961, by B. Deradoorian, H. M. Smith, and R. R. Thompson.

Preferably the ends 33 and 34 are cut perpendicular to the longitudinalaxis of the array after the individual tubes have been fused togetheralthough spherical cuts A conductive coating 33a and 34a is appliedrespectively to ends 33 and 34, so that all, of the resistive coatingsare connected'together electrically. Coating 33a is connected to anegative voltage such asminus 1000 volts and coating 34a is connected toground. When a source 35 of particles to be multiplied is placed at end33 and a collector of multiplied particles 36 is placed at end 34 ofarray 31, the effect is to reduce the source. size correspondingly sothat if sourcev 35 were a photocathode in an image intensifier andcollector 36 were a phosphorus screemthe image on photocathode 35 wouldbe reduced in size, butmuch more intense on screen 36. If source 35 werereversed in position with collector 36, then the effect would bereversed and the area of incoming particles would be enlarged at theoutput end.

Further embodiments which employ tapered sides for onlyla portion ofthe, individual tube lengths may also be used to advantage asillustrated in FIGURE 4,where a plurality of individual tubes 40, eachhaving an outer layer41 of insulative material and an inner layer 42 ofresistive material is funneled at end 4 3only. A source 44 is placed at.end 43 and a collector 45 is placed at the opposite end. By soplacingthe individualchannels 40 and so forming the tunnels, the multiplyingefiiciency is not only increased due to the aforementioned higherprobability of electron imp-act on the secondary emission surface, butthe channel wall thickness is decreased at end 43 so that there is moreopen area and a higher percentage of incoming electrons or otherparticles arev received by the channels. There is sufiicient wallthicknessofthe glass tubes 41 towards the non-funneled end to offeradequate support. to the individual channels. Conductive coatings 43a.and 44a are plated onthe ends of the array and the battery connectionsare made thereto.

For certain applications it may be desirable to form a funnelrfl arechannel with both ends of the channel beinglarger than an intermediatechannel area to. provide a tube that can be reversed and an input placedat either endwith a collector at the other end- .This isshown in FIGURE6 where glass tube 50 has a funnel 51 and a flare 52 beinglonger. Abattery 53 places a potential across the continuous resistive, secondaryemissivecoating 54 on glass tube 50. fIncoming particles 55 strike theWalls: of' funnel 51-to improve multiplication while the longer flare 52has a larger opening .to providemagnification. i

This invention may also be used to provide increased signal carryingcapabilities. By forming a flared portion at the output ofa straightsection, the area against which electrons .may impact-is substantiallyincreased thereby reducingelectron density near the secondary emissivesurface to improve multiplication. Y

Although this invention has been-disclosed and illus-' trated withreference to particular applications, the i applications which will beapparent to persons skilled in the art. The invention is, therefore, tobe limited only as indicated by the scope of the appended claims.

Having thus described our invention, We claim: 1. A multipliercomprising receiving means, collecting means, i a V W-all means beingatleast partially'provided with secondary emissive material and definingat least a partially enclosed multiplying path having its longitudinaldimension between said receiving means and collecting means, a saidmultiplying path being totally clear of field producing physicalobstructions independent of said wall means, sa-id wall means having atleast a portion thereof nonparallel to said multiplier longitudinalaxis, means for establishing a continuous potential gradient along saidlongitudinal dimension, said last means establishing a total'electricfield which is angularly related to the longitudinal axis corresponding-to the wall means angular relation to said longitudinal axis. .2. Themultiplier of claim 1 wherein,

said wall means defines a cylindrical channel, said channel having atleast a portion of its interior surface funneled, said electric fieldbeing funnel shaped at the funnel shaped portion of saidlchannel. .3.The multiplier of claim lwherein,

said wall means has portion where sides are. parallel and a portionwhere the sides are divergent. 4. The multiplier of claim 1 wherein,

said wall means having sides convergent along the entire length thereof,said electric ,field-being convergent along the entire length thereof; 7V 5. The multiplier of claim 4 wherein, a plurality of multipliers havethe outer surfaces of their wall means fused together to form an array.6. The multiplierof claim 3 wherein,

a plurality of multipliers havethe outer surfaces of their wall meansfused together toform an array. 7. The multiplier of claim 1 wherein,the cross section of said wall means. throughout th length thereof issubstantially circular. 8. The multiplier of claim 7, V a where saidwill means are first convergent and then divergent to provide afunnel-flare.

No references cited.

1. A MULTIPLIER COMPRISING RECEIVING MEANS, COLLECTING MEANS, WALL MEANSBEING AT LEAST PARTIALLY PROVIDED WITH SECONDARY EMISSIVE MATERIAL ANDDEFINING AT LEAST A PARTIALLY ENCLOSED MULTIPLYING PATH HAVING ITSLONGITUDINAL DIMENSION BETWEEN SAID RECEIVING MEANS AND COLLECTINGMEANS, SAID MULTIPLYING PATH BEING TOTALLY CLEAR OF FIELD PRODUCINGPHYSICAL OBSTRUCTIONS INDEPENDENT OF SAID WALL MEANS,